The present invention relates to a fixing structure, a lens block, an image reading unit and an image forming apparatus used in a copying machine, a facsimile, a scanner and so on.
Conventionally, a lens block of an image reading unit used in, for example, a copying machine, a facsimile and a scanner device includes a base member, an imaging lens system mounted on the base member, and an image sensor which is attached to the base member and which has a line photoelectric transducer and a package accommodating the line photoelectric transducer. The lens block of the image reading unit moves an illumination light source for a manuscript in a sub-scan direction, reduces and images the light reflected from the manuscript on the line photoelectric transducer through the imaging lens system comprising more than two groups of lenses, and photo-electrically converts an imaging light flux imaged on the line photoelectric transducer into image reading signals to output the converted image reading signals.
In the lens block of the image reading unit, a read image is degraded when the imaging light flux is misaligned in an optical-axis direction on a light-receiving surface of the line photoelectric transducer. Accordingly, a distance between each lens group is adjusted such that the read image satisfies a design standard.
Also in the lens block of the image reading unit, a central rectangular part within a surface of lenses structuring a lens group contributes to the imaging of the line photoelectric transducer. The imaging performance such as an aberration in the rectangular part of the lens varies in a circumferential direction of the lens around an optical axis of the lens as the center. Therefore, even when the lens is positioned such that the rectangular part of the lens becomes parallel to the line photoelectric transducer and a distance between the lens and the line photoelectric transducer is adjusted so that an imaging position of the imaging light flux is imaged or positioned on the light-receiving surface of the line photoelectric transducer, the imaging position of the imaging light flux may be misaligned in the optical-axis direction on the light-receiving surface of the line photoelectric transducer if the lens is set by rotating the lens in order that the rectangular part is in parallel with the line photoelectric transducer, causing the degradation of image quality.
Particularly in the lens used in the lens block of the image reading unit for reading a color image, the color image cannot be reproduced well when imaging positions of respective blue wavelength, green wavelength and red wavelength are misaligned in a rotation direction of the lens. Hence, it is also necessary to adjust the lens in the circumferential direction of the lens around the optical axis as the center.
Accordingly, the optical axis of the light reflected from the manuscript and entered through the lens groups and the optical axis of the line photoelectric transducer must be positioned on the same line. Given this factor, there is a fixing structure of a lens used in a lens block of the image reading unit, in order to position and fix the lens.
A conventional lens block of an image reading unit is provided with a chassis, a lens and a pair of intermediate retaining members. The chassis is formed in a rectangular shape, and is positioned so that both surfaces of the chassis follow along an optical axis of the light reflected from the manuscript. Both surfaces of the lens are in a circular arc shape, and the lens is formed in a cylindrical shape having a thickness in an optical axis direction. In addition, the lens is positioned in the chassis so that an optical axis of the lens follows along the optical axis of the reflected light. Each of the intermediate retaining members includes a first mounting surface and a second mounting surface, and is formed in an “L”-like shape. The first mounting surface and the second mounting surface are perpendicular to each other.
The first mounting surface of the intermediate retaining member and a side surface of the lens are mutually fixed by an adhesive, and the second mounting surface of the intermediate retaining member and the chassis are mutually fixed by the adhesive. Since the chassis and the lens are fixed via the intermediate retaining member, the optical axis of the light which is reflected from the manuscript and entered thorough a lens group and a position of a line photoelectric transducer are adjusted.
In addition, in the above-described imaging reading unit, it is also necessary to position and fix the imaging lens and the photoelectric transducer, etc. with high precision in order to locate an image imaged by the imaging lens system on the photoelectric transducer and to read optical characteristics such as focus and magnification with predetermined required precision.
Conventionally, fixation utilizing a screw is used for fixing the imaging lens and the photoelectric transducer and so on. However, since an amount of displacement in the fixation by the screw is too large, i.e. more than 30 μm, the screw fixation raises problems in fixing of the photoelectric transducer which requires positioning precision of a few μm levels.
Accordingly, in a structure such as the image reading unit in which the high-precision positioning mentioned above is required, conventionally, mutual members are fixed by an adhesive to reduce the amount of displacement between the members.
However, in the lens block of the above-described image reading unit, the lens attached to the chassis of the lens block cannot be removed easily. Hence, it is difficult to reuse the removed lens or perform separate collection of resources.
In addition, in the lens block of the image reading unit having a fixing structure of a lens cylinder, it is difficult to remove the lens cylinder adhesively fixed on the base member from the base member when a mounting position between the base member and the lens cylinder is misaligned. Accordingly, it is also difficult to reuse the lens block and collect the resources separately when the mounting position between the base member and the lens cylinder is misaligned.
Furthermore, the adhesive used in the fixation of the mutual members in the image reading unit is generally difficult to liquefy or levigate again once it is cured. Accordingly, when the mutual members are fixed by the adhesive as described above, it is difficult to remove the mutually fixed members or attach them again after the adhesive is once cured.
More specifically, in the fixing structure of, for example, the base member as a first member and the package as a second member in the above-described image reading unit, they can be easily removed by using a screwdriver when the members are mutually fixed by the screw, in a case where a defective product having defective positioning precision between the members for example is produced. However, since both members such as the base member and the package cannot be removed from each other if they are fixed by the adhesive, both of the base member and the package have to be discarded, which means that, even though the most expensive component in the image reading unit is a circuit board having the photoelectric transducer, the expensive circuit board also have to be discarded due to the defective positioning accuracy between the members, despite the fact that the circuit board has a normal function. Such a circumstance not only invites high expense but also it is undesirable in terms of resource saving. Additionally, the circumstance causes rise in recycling costs of components as well.